1. Field
Apparatuses and methods consistent with exemplary embodiments relate to depth image acquisition acquiring depth information by using a rolling shutter method.
2. Description of the Related Art
Recently, three-dimensional (3D) cameras or light detection and ranging (LIDAR) techniques for capturing distance information of an object have been researched. One of these research techniques is a time-of-flight (TOF) method that measures a traveling time of light, whereby a distance between an image capturing unit and a subject is measured to generate a depth image.
In the TOF method, light of a predetermined wavelength, for example, near-infrared (NIR) (850 nm), is projected to a subject by using a light-emitting diode (LED) or a laser diode (LD), and light of the same wavelength reflected on the subject is measured or captured by using a photodiode or a camera to thereby extract a depth image. A TOF method may include a series of various optical processes, such as projection of light from a light source, reflection of a subject, optical modulation, capturing, and processing.
For example, an optical shutter method is a method in which light of a predetermined wavelength (e.g., NIR 850 nm) is projected to a subject by using an LED or LD and an optical image obtained from light of the same wavelength reflected on the subject is optically modulated by using an image intensifier or a predetermined solid state modulator. Furthermore, in the optical shutter message, an image is captured by using an image sensor, such as a photodiode (PD), a charge-coupled device (CCD), or a complementary metal oxide semiconductor (CMOS) image sensor (CIS), included at a rear end of the image intensifier or the solid state modulator and an intensity value of the image is processed so as to obtain a depth image.
The CCD is a device in which metal-oxide-silicon (MOS) capacitors are very closely positioned and charge carriers are transferred to and stored in the MOS capacitors. The CIS is a device in which MOS transistors corresponding to the number of pixels are formed by using CMOS technology and a control circuit and a signal processing circuit are used as peripheral circuits. Furthermore, the CIS uses a switching method of detecting outputs in turn by using the MOS transistors.
The CCD has received attention as a leading image sensor and is widely used in digital cameras, camera phones, etc. As the importance of camera phones increases, it is important to reduce the power consumption of camera phones. Thus, there is an increasing interest in the CIS. The reason is because the CIS is manufactured by using CMOS technology, which is used for manufacturing general silicon semiconductor devices, and therefore has a small size, a low price, and low power consumption.
Examples of a method of capturing an optical image of a subject, formed in an image capturing region of an image capturing device, include a global shutter method and a rolling shutter method. The global shutter method is a method in which all pixels in the image capturing region capture an optical image at the same time. On the other hand, the rolling shutter method is a method in which one or several pixels in the image capturing region sequentially capture an optical image.
Both the global shutter method and the rolling shutter method may be applied to a CMOS image capturing device. When the global shutter method is applied to the CMOS image capturing device, a captured image is not transformed even if a subject moves, because all pixels capture an optical image of the subject at the same time. On the other hand, in a CMOS image capturing device using the rolling shutter method, an image may be distorted due to a difference in image capturing time for each scan line because one or several pixels sequentially capture an optical image.